Studying Same-Sign Top Pair Production in Flavor Changing Scalar Models at the HL-LHC.

We investigate the potential of the HL-LHC for discovering new physics effects via new strategies in the same-sign top pair signatures. We focus on the semi leptonic (electron and muon) decay of the top quarks and study the reach for a simplified model approach where top quark flavor changing could occur through a neutral scalar exchange. A relatively smaller background contribution and clean signature are the advantages of the leptonic decay mode of the same-sign $W$ bosons in the same-sign production processes of top quark pairs. Assuming the FCNC between top quark, up type quark and scalar boson from the new physics interactions the branchings could be excluded of the order ${\cal O}(10^{-4})$. We use angular observables of the same-sign lepton pairs and the top quark kinematics in the process which provide the possibility of separation of new physics signal from the SM backgrounds as well as distinguish the $tuh$ and $tch$ couplings. We find that the same-sign top quark pair production is quite capable of testing the top FCNCs at the HL-LHC.